Sigwart succeeded in implementing the first surgery of coronary artery vascular stent in 1987. After that, coronary artery stent has been widely accepted as the second milestone in the history of interventional therapy of coronary heart diseases.
Common metallic stents are produced from 316L stainless steel, cobalt chromium alloy or nickel titanium alloy. Although these metallic stents meet the requirements of mechanical properties in the structure, they contact directly with blood after implanted into the human body, which stimulates the rejection capability of the human body to foreign matters, causing hyperplasia of the vascular intima tissue and the smooth muscle cells. Moreover, as the stent surface gets rougher, the possibility of cruor occurring gets larger. Metallic stents also release heavy metal ions under blood circulation, and these heavy metal ions would promote happening of thrombus. These factors lead to happening of restenosis after the stent implantation.
In this case, drug-eluting stents have been developed as required. The drug is coated onto the metallic stent through some processing, and after the stent is implanted into the body, the drug can be released at the region of lesion, maintaining a releasing period, which effectively prevents post-operative restenosis in-stent. However, most of the present drug stents are coated with drug on both the interior and exterior metallic surfaces, so as to render high drug concentration inside the blood vessel and high releasing rate, and the releasing direction cannot be controlled effectively, making some of the drug can not be absorbed by the blood vessel wall. Besides, at the places where the stent shape changes relatively largely, the coating herein will easily fall off during the process of stent propelling and expansion. The fallen drug mass flows with blood, and easily causes thrombus, leading to new damages.
So far there are already vascular stent with drug-carrying slots on the market, and the vascular stent normally has a net tube shaped structure, comprising a plurality of main structure struts with sinusoidal waveform structure. The adjacent main structure rods are connected there between with connecting rods, and the exterior surface of the main structure rod has drug-carrying slots. This vascular stent with drug-carrying slots can improve the distribution of the drug in the blood vessel, increase the adhesion capability of the coating on the stent, and prolong the functioning time of the drug. However, the length of the drug-carrying slots is very important. If the length is too short, it will cause nonhomogeneous distribution of the drug in the slots, and the drug loading cannot meet the requirements for effective cure of lesion; if the length is too long, it would surely affect the mechanical property of the stent, causing fracture of the stent.